Trajectory guide



pri 23, w53 R. G. ALLEN, JR

TRAJECTORY GUIDE Filed May 19, .1961

m@ Wk nm nml En mw \NN .i i l United States Patent M' 3,086,705 TRJECTORY GUDE Ralph G. Allen, Er., 310 Rillar Vista Drive, San Antonio, Tex. Filed May 19, 1961, Ser. No. 111,384 2 Claims. (Ci. 23S-61.5)

This invention relates to a shooting aid, and, more particularly, to a device for the rapid and graphic determination o the relation of the trajectory of a projectile or projectiles from a lirearm with respect to a line of sight from the rearm. The line of sight may be that established with telescopic sights, iron sights, or the bore of the firearm. The device is particularly useful as an aid to hunters and Sportsmen in facilitating accuracy of tire at ranges other than the sight-in range.

The principle used in the design and construction of the invention can be applied to any type and caliber of firearm-piston, rifle or shotgun-tiring any type of projectile for which the trajectory can be determined, either experimentally or through calculations.

in recent years the necessity for understandingY and applying basic ballistic principles has increased due to the large number of new rilies and small arms available to the hunter and sporting enthusiast. This need has been recognized by leading sports magazines and gun digests, which have attempted to enlighten the shooting enthusiast by publishing articles discussing and evaluating ballistic data presented in the vform of graphs and tables. Al-

though these graphs and tables, when available, will provide an over-all basis for selecting a particular type of shell or caliber of firearm, they do not provide a handy and simple means for solving specific ballistic range problems encountered by the hunter in the lield. Such problems are readily handled by the device of the present invention.

A primary object of the invention is to provide a device which will enable the `shooter to determine how to aim his lirearm in order to place the bullet on target at some given range.

Another object of the invention is to provide a small, compact device which will enable the user to determine the most optimum sight-in range for a firearm.

lt is also an object of the invention to provide a simple calculating device which will permit a hunter on the spot to determine how high or low he should aim with respect to a selected target when shooting at ranges different from his established sight-in distance.

A further object of the invention is to provide a durable, pocket-size calculating device of the type described, having only one movable member which will facilitate easy handling and quick use.

The device, in its broad aspects, comprises a base member or card of convenient size having indicia displayed thereon providing a graphic representation of a trajectory curve in combination with a cooperating movable member, providing a simulated line of sight, pivotally engaged with the base member and so oriented with respect to the indicia on the base member that the simulated line of sight may be rotated about the pivotal axis to intersect the trajectory curve at a point representative of a selected sight-in range; and when so positioned, the distance between the trajectory curve and line of sight at all other ranges will represent the rise or drop of the projectile with respect to the line of sight. The pivot 3,@865 Patented Apr. 23, 1963 point for the line-of-sight member is located at approximately that point on the base member marking the beginning of the trajectory curve, i.e., representing the muzzle of the rearm.

The objects and advantages of the invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of one form of the trajectory guide of the invention, showing the movable line-of-sight member rotated to intersect a projectile curve ata sight-in range or" 350 yards;

FIG. 2 is an end view of FIG. l; v

FIG. 3 is an enlarged, detailed View illustrating the manner in which the movable member may be pivotally connected to the base member so a-s to provide an adjustment for different types of sights; and

FIG. 4 is the end view of a modilication of the device of FIG. l, illustrating a plastic coating for the base member.

Referring now to the drawings, there is shown in FIG. 1 a base member l0, having a rectangular outline, on which indicia are printed or otherwise displayed representative of a series of parallel drop scales 12 oriented with respect to a line of departure 14 so as to present the drop in inches a projectile will encounter after being fired from a rifle having a muzzle position i5. The line of departure 14 indicates the direction the projectile would take if there were no gravity or Wind resistance to alter its path. A pair of trajectory curves 16 and 18 displayed on the base member 10 show the paths of projectiles being fired from the muzzle of a rifle located at the origin 15 of the line of departure. The trajectory curves 16 and 1S are representative of the paths taken by bullets of different types of cartridges tired from the same caliber gun. It will be understood that one or a plurality oftrajectory curves may be displayed on a single device.

A transparent movable member 20, which provides indicia 2l representative of the line of sight, is pivotally connected to thebase member 10 to rotate about an axis 22 offset from the point 1S by a distance equivalent to the height of the gun sight above the bore of the gun. Reasonably good accuracy can be obtained, however, when the pivot point 22 and departure point l5 approximately coincide. The indicia line 21, in the device illustrated, is provided on a clear plastic background 20. Alternatively, a straight line having a pivotal axis at point 22 may be provided by use of a wire or metal strip.

In the device illustrated, the line-of-sight member 20 is pivotally connected to the base member 10 by a metal eyelet 23 which extends through a corresponding bore in member 20 and through a slot 24 (FIG. 3) in base member 1t). The pivotal connection may be slid from one end of the slot to the other, toward the respective arrows displayed on base member 10, depending on whether the line of sight is to represent that .through telescopic or iron (sights. A small plastic washer 2'5 is provided on the opposite side of base member 10 from pivotal member 20. The pivotal conection may be suiliciently tight as to maintain the pivot point at a selected position by friction and yet permit it to be moved when desired. The origin of the telescopic line of sight at the firearm is taken to be, on the average, 11/2 inches above the bore-sight line. The origin of the line of sight for iron sights is taken to be on the average 3A inch above the bore-sight line. Although it is preferred to provide `a sliding pivotal connection so that the trajectory guide may be readily adaptable for each type of sights, a trajectory guide for each type of sight may be constructed by using a tixed pivot. Moreover, by selecting a point intermediate the two extremities of slot 24 as a fixed pivot, a trajectory guide may be made for all types of sights, sacrificing some accuracy. The display of scales and trajectory curves are oriented at an angle of approximately 45 with respect to the base of the background board. This permits the entire curve for practical range of the firearm to be displayed on a small pocket-size card, i.e., the card space is utilized to maximum advantage. A set of instructions is located in the upper right-hand corner of lthe base member to allow the user to quickly familiarize himself with the simple operating procedures to facilitate rapid manipulation.

As is evident from the foregoing description, the trajectory guide may be constructed from any type of material such as paper, cardboard, wood, composition board, plastic or composition material, metal or photographic materials, upon which can be drawn, inscribed or printed the necessary scales, graphs, curves, tables, data and information. FIGURE 4 illustrates an embodiment in which a cardboard base is coated with a transparent plastic film or envelope 26, providing a waterproof durable device.

The trajectory curves and ballistic data are computed from published values of projectile velocity as 1a function of range (or from experimental measurements of projectile velocities), by use of ballistic tables and standard computational techniques such as Hatchers Notebook, 2nd edition. published by Stackpole Company, 1957. The movable pivot for the line of sight is incorporated in order to account for the position of the line of sight above the bore of the firearm and is scaled to represent the average distance above bore for telescope or iron sights.

As previously mentioned, brief operating instructions may be printed on the trajectory guide. A more detailed set of instructions is given below in order to insure a clear understanding of its operation:

Select a trajectory guide for the type of firearm concerned. (The curves in the device illustrated in the drawing are for a 243 Winchester riile using two commercially available types of cartridges.) Identify the trajectory curve which corresponds to the bullet type and weight, and cartridge loading concerned. Push line-of-sight pivot toward point of arrow which identifies the type of sight involved. Holding line-of-sight pivot in this position with thumb of left hand, swing -line of sight until it intersects selected trajectory curve at the sight-in range. (The sight in range is that distance for which the rearm sights have been adjusted to place bullets on target, or the range at which it is desired that the firearm place bullets on target.) With the line of sight positioned with the thumb of the right hand so that it intersects the trajectory curve at the sight-in range, the bullet rise or drop may be observed from me scale distance between the selected trajectory curve and the line of sight, measure along the grid lines. Each small division of the grid lines may be scaled to represent one inch, so that the bullet drop or rise in inches is given by the number of scale divisions between the trajectory curve and the line of sight-at any range desired.

The trajectory guide may be used to solve many practical problems encountered by the shooting enthusiast while at home or in the field. Examples of these are as follows:

EXAMPLE l Suppose the rifle of interest is equipped with a telescope and that this rie is zeroed in so that it is on-target at 350 yards. The question is =where will the bullet hit at a range other than 350 yards. FIG. l has been drawn to illustrate this example.

(l) Push the line-of-sight pivot 22 toward the point of the arrow marked "telescope.

(2) Swing the line-of-sight member 20 until line of sight 21 intersects the trajectory curve for the cartridge involved at 350 yards (curve i8 in this instance is intersected at point 30).

(3) The distance between the line of sight 21 and the trajectory curve, measured along the grid lines 12 to the right of point 30 gives the bullet drop at ranges above 350 yards and to the left of the point 3() gives the bullet rise for ranges below 350 yards.

At a distance of 500 yards (sight-in at 350 yards), the bullet gr. Win. Se Rem.) will be approximately 25 inches below the telescope line of sight. At a distance of yards from the muzzle (1/2 the sight-in distance in this case) the bullet will be approximately 7 inches above the telescope line of sight. Thus, in shooting at an object 500 yards away, the hunter should aim about 25 inches above lthe point he wishes the bullet to hit. ln shooting at an object 175 yards away, the hunter should aim 7 inches below the point he wishes the bullet to hit.

EXAMPLE 2 Determining the Best Sight-In Range Select the maximum height above the line of sight that you wiil tolerate. This selection will be more or less arbitrary and depends upon the size of the object, or the size of the area on the object in which you desire hits. Then adjust the line of sight so that this limiting height is not exceeded throughout the trajectory. The greatest sight-in range possible without exceeding the limit selected for rise will be the best sight-in range for the riflecartridge combination concerned. lf, in addition, a maximum permissible drop below the line of sight is selected, the maximum range for Ywhich this particular sight in range is acceptable may be established as `that range at which the drop equals, but does not exceed, the selected maximum permissible drop.

EXAMPLE 3 Sighting-In for Large Distance Using a Short Range Suppose only a 10G-yard range is available but you desire to sight-in your rie at 250 yards. Using the trajectory guide, select proper pivot point for the line of sight. Set the line of sight to intersect the appropriate trajectory curye at the desired sight-in range. Read the rise of the bullet above the line of sight at the range which corresponds to the distance available for sightingiri. Adjust your rie to re high, at the sight-in range available, a distance in inches equal to the bullet rise indicated by the trajectory guide for the available sight-in distance. The rie should then be on target at the de sired longer range.

It is readily apparent from the above examples that the invention solves many of the shooting enthusiasts problems and provides a compact and easily operated device.

I claim:

1. A device for determining the departure of a rearm projectile from a shooters line of sight, comprising a flat base member having a series of linear drop scales arranged in parallel thereon, said drop scales being spaced so as to represent various range distances, a trajectory curve intersecting said scales at points which indicate the drop of a projectile from its line of departure at a certain range, a movable member providing a line of sight pivotally connected to said base member at approximately the origin of said trajectory curve so that an intersection of said line of sight with the trajectory curve may be provided at a selected sight-in range of the tirearm and the distance between said curve and said line of sight along said drop scales at other ranges is a measure of the rise or drop of the projectile with respect to said line of sight, the pivotal connection of said movable member to Said base member including a pivot slidably mounted with respect to said base member for 6 movement between a first position representing the dis- References Cited in the le of this patent tance of a telescopic sight above said origin of said UNITED STATES PATENTS curve and a, second position representing the distance of an iron sight above the origin of said curve. 1,290,343 Posner Jan 7 1919 is in the form of an elongated rectangle of pocket size,

the ori-gin of said trajectory curve is located near the FOREIGN PATENTS lower lift hand corner of said base member with the line 120.247 Great Britain Oct. 29. 1918 of departure extending toward an upper mid-portion of said base member, and the drop-scales are oriented at 10 right angles to the line of departure from said origin. 

1. A DEVICE FOR DETERMINING THE DEPARTURE OF A FIREARM PROJECTILE FROM A SHOOTER''S LINE OF SIGHT, COMPRISING A FLAT BASE MEMBER HAVING A SERIES OF LINEAR DROP SCALES ARRANGED IN PARALLEL THEREON, SAID DROP SCALES BEING SPACED SO AS TO REPRESENT VARIOUS RANGE DISTANCES, A TRAJECTORY CURVE INTERSECTING SAID SCALES AT POINTS WHICH INDICATE THE DROP OF A PROJECTILE FROM ITS LINE OF DEPARTURE AT A CERTAIN RANGE, A MOVABLE MEMBER PROVIDING A LINE OF SIGHT PIVOTALLY CONNECTED TO SAID BASE MEMBER AT APPROXIMATELY THE ORIGIN OF SAID TRAJECTORY CURVE SO THAT AN INTERSECTION OF SAID LINE OF SIGHT WITH THE TRAJECTORY CURVE MAY BE PROVIDED AT A SELECTED SIGHT-IN RANGE OF THE FIREARM AND THE DISTANCE BETWEEN SAID CURVE AND SAID LINE OF SIGHT ALONG SAID DROP SCALES AT OTHER RANGES IS A MEASURE OF THE RISE OR DROP OF THE PROJECTILE WITH RESPECT TO SAID LINE OF SIGHT, THE PIVOTAL CONNECTION OF SAID MOVABLE MEMBER TO SAID BASE MEMBER INCLUDING A PIVOT SLIDABLY MOUNTED WITH RESPECT TO SAID BASE MEMBER FOR MOVEMENT BETWEEN A FIRST POSITION REPRESENTING THE DISTANCE OF A TELESCOPIC SIGHT ABOVE SAID ORIGIN OF SAID CURVE AND A SECOND POSITION REPRESENTING THE DISTANCE OF AN IRON SIGHT ABOVE THE ORIGIN OF SAID CURVE. 